A 1994 neuroscience graduate from Duke University, Craig Savage chose to share his love of biology and psychology as a teacher. For almost 20 years, he has taught Advanced Placement Biology and Psychology in independent schools in Atlanta, GA. and Dallas, TX. With a “simpler is better” approach, Craig’s lessons have helped thousands of students in over 190 different countries excel on their high school, AP and college exams.

Learn about glycolysis and its role in producing ATP and pyruvate during cellular respiration. The first of three, this lesson will teach you the formula for cellular respiration and how glucose is broken down for use in the Kreb’s cycle and fermentation.

For information on the next two stages of cellular respiration, watch “Cellular Respiration: The Kreb’s Cycle” and “Cellular Respiration: Electron Transport Chain Phosphorylation.”

Learn about the Kreb’s cycle and its role in producing ATP and high energy NADH and FADH during cellular respiration. The second of three, this lesson will teach you how the Kreb’s cycle converts pyruvate that was produced during glycolysis into ATP and high energy NADH and FADH for use in electron transport phosphorylation.

For an introduction to glycolysis, watch the first lesson in this series: “Cellular Respiration: Glycolysis.”

Learn about electron transport phosphorylation and its role in producing ATP during cellular respiration. The last of three, this lesson will teach you how the electron transport chains in the mitochondria leverage high energy NADH and FADH2 to aerobically produce 30+ molecules of ATP.

For an introduction to the first two stages of cellular respiration, watch: “Cellular Respiration: Glycolysis” and “Cellular Respiration: The Kreb’s Cycle.”

Learn about fermentation and its role in producing ATP under anaerobic conditions. A complement to Craig’s series on cellular respiration, this lesson will teach you how alcoholic and lactic acid fermentation replace cellular respiration to produce ATP when oxygen is unavailable.

For a review of glycolysis, please watch “Cellular Respiration: Glycolysis."

Learn how scientists discovered DNA and determined its function, composition, and structure. The first in a series of eight, this lesson will teach you about the major experiments that led to our understanding of DNA as the physical basis for heredity. Craig will also teach you about the chemical structure of DNA and recent advances in genetic study - including cloning Dolly the sheep!

Watch the rest of this series to learn about DNA replication, protein synthesis, and gene control.

Learn about DNA, the complex molecule that serves as the foundation for all living organisms. The second in a series of eight, this lesson will teach you how nucleotides combine to form the DNA ‘ladder’ structure. Craig Savage will also teach you how this ‘ladder’ spirals to create a double helix, and interacts with proteins to form chromosomes.

Watch the rest of this series to learn more about DNA replication and protein synthesis.

What is DNA replication? Learn how nucleotides bind to form new strands of DNA - creating a replica (or identical copy) of a cell’s genetic material. The third in a series of eight, this lesson teaches you the differences between leading and lagging strands of DNA, how RNA primer works, what causes DNA mutations, and more.

To better understand the basic structure of DNA, be sure to review “The Structure of DNA.” Watch the rest of this series to learn about protein synthesis and gene control.

Are you a high school student learning about DNA and RNA for the first time? Or maybe you are in college and it’s been a few years, and you are a little rusty on biology. Maybe you are just a curious soul? Whichever it is, this lesson on RNA and protein synthesis explains the three forms that RNA takes, and the role that each plays in the steps of protein synthesis. Learn how to use a codon chart and ultimately how to determine the amino acid that an RNA sequence codes for.

Did you know that when RNA is made from a DNA strand, it contains extraneous information that is edited out of the final RNA sequence? In this second lecture in his biology series on RNA, Craig Savage explains the first step of protein synthesis: transcription. Learn about the four steps of the transcription, and how enzymes “edit” the pre-mRNA. Once you’ve got a handle on transcription, you’ll be all ready for the second step of protein synthesis: translation.

Once a mature strand of mRNA is ready to leave the nucleus, it goes to the ribosome for translation. But what happens at the ribosome? Learn about the second phase of protein synthesis (translation) in this installment of Craig Savage’s series on RNA. Build on material covered in previous tutorials to understand the role of peptide bonds and polysomes in this simultaneously incredible and also commonplace biological process.

How can liver and blood cells have the same DNA but different functions? In this seventh of eight lessons on DNA and protein synthesis, learn how cells use two different mechanisms to control gene expression: cell differentiation (in which part of the DNA molecule is restricted from protein transcription), and moment-to-moment adjustments (in which cells regulate outputs in response to environmental conditions and internal or external signals).

In this final of eight lessons on DNA and protein synthesis, learn how prokaryotes (such as bacteria) regulate gene expression and maintain the cell’s homeostasis. Follow along with Craig Savage as he teaches you about prokaryotic genetic operons, and how they interact with molecules like tryptophan, CAP, and mCAP to create feedback loops that control RNA replication and regulate protein synthesis.

Why in the world do snakes have hipbones? In this biology lesson, allow Craig Savage to blow your mind with evidence for evolution backed by evolutionary theorist Charles Darwin. Discover claims that support natural selection such as biodiversity, biogeography, and vestigial structures. See images of embryo development that reveal how humans, at one point in their lives, look like fish! Not convinced? Keep watching to see how the process works.

If you are in biology now, or at one time were, you probably know that Darwin is credited with developing the theory of natural selection. But Darwin wasn’t the first to consider the possibility of evolution. Darwin based his work off of the work of Jean Baptiste Lamarck (who proposed that species change based on need), and even geologic and economic principles. Perhaps we could say Darwin’s theory (supported by so much information) was the “fittest,” because it is the theory that survived.

Natural selection is the process by which evolution occurs—an example of this is the classic case of the Peppered Moth. But this particular case is called directional selection; natural selection operates in three other ways, and can even explain why some species (like sharks, crocodiles, and ferns) have not changed in thousands of years. Learn how the environment selects for a specific trait, over time changing, or not changing, the genetics of an entire population.

Darwin’s finches played a large role in his development of the theory of evolution by natural selection. What Darwin had thought were variations of the same bird were actually multiple species of different birds. But evolution takes millions of years to occur—how did the twelve species of Darwin’s finches all diverge from one species of bird? In this third of five lessons on evolution from Craig Savage, learn about the two factors that allow for speciation: reproductive isolation and time.

You are probably familiar with the concepts of natural selection and adaptation, but how do actual genetic changes occur within an entire species? In this fourth lesson in his series on evolution, Craig Savage explains population genetics; defining basic terms before demonstrating with a Punnett square how to determine the genotype frequencies within an entire population. Learn what the Hardy-Weinberg principle is, and how it can help determine why population changes occur.

In this second part of his lesson on population genetics, Craig Savage explains how natural selection affects gene pools. Build on your knowledge of the Hardy-Weinberg principle to understand how violations of the principle lead to genetic changes within a population. Craig demonstrates genotype frequencies, and how bottlenecking can lead to dramatically different allele frequencies for smaller populations versus larger populations (upon whom this example of genetic drift effects little change).

Where and how did life on earth originate? Explore various theories with Craig Savage in this fifth and final lesson in a series on evolution. Was earth seeded by microbes from outer space, as in the panspermia theory? Or could organic compounds have formed in earth's primordial sea, through the process of chemical evolution? Learn about the necessary steps along the path to creating life, and experiments that test the Oparin-Haldane hypothesis.

The first in a series of five, this lesson teaches you about the basic laws of Mendelian genetics. Through his many pea plant experiments, Gregor Mendel was able to shape our understanding of how genes are passed down and expressed from one generation to the next. Learn about his theories on genetics and heredity, including: dominant gene traits, phenotypic expression of genes, and how to use a Punnett square to determine inheritance patterns.

Expand your understanding of genetics by learning how variations on Mendel’s theories predict the heredity of skin color, eye color, and balding in humans. The second in the series of five, this lesson introduces the topics of: incomplete dominance, co-dominance, multiple alleles, and linked genes. It also discusses how the expression of genes - or phenotype - is affected by pleiotropy, polygenics, and environmental influences.

Learn about sex-linked genetic traits and homologous chromosomes - and discover the connection between white-eyed fruit flies and hemophilia in the royal family. The third in the series of five, this lesson details the discovery of sex-linked traits by Thomas Hunt Morgan, and explains the difference between autosomal homologous chromosomes and the X- and Y-chromosomes. Practice your Punnett square skills to determine phenotypic ratios, and learn what it means to be a carrier for a genetic trait.

Learn the causes behind genetic mutations that can occur at the DNA and chromosome levels - and how they can lead to conditions such as Down’s Syndrome. The third in the series of five, this lesson will teach you about DNA level mutations like base substitutions, insertions, and deletions, and how they can alter the protein amino acid sequence. Also, explore chromosome mutations such as non-disjunction, and discover how these mutations can cause conditions such as Down's and Turner's Syndrome.

The last in a series of five, this lesson wraps up the discussion on genetics, inheritance, and mutations by describing genetic disorders such as sickle cell anemia, Huntington's disease, hemophilia, and others. Learn about different hereditary patterns for these genetic disorders and how you can use a pedigree to study and predict human genetic outcomes.

The first in a series of five, this lesson gives you an introduction to photosynthesis and teaches you how plants take energy from the sun and convert it to glucose using chlorophyll. Learn about light reactions, the calvin cycle, and the equation for photosynthesis that details how reactants in photosynthesis combine to form the energy necessary to sustain plant life.

Be sure to watch the next four lessons in this series for more information about photosynthesis.

The second in a series of five, this lesson teaches you about photosynthesis and goes into detail about how plants take carbon dioxide and energy from the sun to generate ATP, NADPH, and oxygen. These light-dependent reactions take place in photosystems within the thylakoid membrane of chlorophyll cells and provide the inputs necessary to generate glucose.

The third in a series of five, this lesson teaches you about the processes that take place during photosynthesis light reactions. Learn how electron transport chains and photolysis create energy by establishing a proton gradient within the thylakoid. This energy is used to drive the phosphorylation of ADP into ATP using ATP synthase.

If you’d like a more general introduction to photosynthesis and light reactions, be sure to watch “Photosynthesis Light Reactions.”

The fourth in a series of five, this lesson teaches you how the Calvin cycle uses ATP and NADPH to generate glucose. A key part in the photosynthesis process, the Calvin cycle takes the products formed during the light reactions, along with carbon dioxide, to form the glucose necessary to sustain plant life.

For a review of photosynthesis and light reactions, be sure to watch “Photosynthesis Light Reactions” and “Chemiosmosis and Photophosphorylation.”

The last in a series of five, this lesson teaches you about carbon fixation pathways that allow plants to effectively process carbon dioxide during photosynthesis. Learn how plant physiology affects the efficiency of photosynthesis and how the C4 and CAM pathways address issues like that of photorespiration.

For a review on carbon fixation during the Calvin cycle, please review “Photosynthesis and the Calvin Cycle.”